This invention relates generally to the manufacture of composite thermoplastic parts such as trim panels for automobile doors and more particularly to a method of manufacturing a composite thermoplastic part that has an integral 360 degree handle.
U.S. Pat. No. 4,459,331 granted to James M. Brix et al Jul. 10, 1984 discloses a composite thermoplastic trim panel for an automobile door that includes an integral loop portion for a 360 degree door handle. The trim panel comprises a molded thermoplastic shell that is fitted with an insert that includes a reinforcement for the loop portion. This subassembly is then filled with a cellular material such as reaction injected foam in a secondary operation to provide a composite trim panel that has a partially formed loop. The loop is completed by cutting an endless hole in the composite trim panel and then attaching plates to cover the foam exposed around the periphery of the hole to provide a finished appearance for the door panel.
While this process is suitable for its intended purpose, the process requires the fabrication of cover plates and the attachment of these cover plates to the trim panel after the endless hole is cut to form the loop.
U.S. Pat. No. 5,173,228 granted to Reza Kargarzadeh, Ken E. Tuttle and John A. Grimes Dec. 22, 1992 discloses another foam in place type method that uses a precast skin shell for forming a 360 degree handle in a composite thermoplastic part such as an automobile door trim panel. In this latter method, the molded thermoplastic shell itself is formed with an integral 360 degree handle in a special mold. The molded thermoplastic shell is then fitted with an insert that includes a reinforcement for the integral 360 degree door handle. The subassembly is then filled with a foam material in a secondary operation to provide the composite door trim panel.
This process is also suitable for its intended purpose. However, the process requires complicated equipment for molding the shell with a 360 degree handle and then a difficult assembly of the handle reinforcement in preparation for the foaming operation.
Automobile interior trim door panels can also be made a vacuum forming process as disclosed in U.S. Pat. No. 4,740,417 granted to Roger Tornero Apr. 26, 1988. In this process, a porous foam backed fabric is loosely positioned over a female mold. A substrate is heated sufficiently to sag and then deposited over the female mold so that the sagging substrate contacts the fabric around an effective mold perimeter. Vacuum applied through the female mold is transmitted through the porous foam backed fabric and attracts the sagging substrate into the mold causing contact and adhesion of the heated substrate and the foam backed fabric. This method produces a contoured door panel that has sizeable functional protrusions, such as an arm rest and ridges or depressions that enhance the decorative appearance of the door. However, the door panel does not have any integral loop portions that provide a 360 degree handle.
It is also known from U.S. Pat. No. 3,467,741 granted to Keith K. Kesling Sep. 16, 1969 to vacuum form an inner panel of a refrigerator door so that wooden reinforcing sticks are embedded in the plastic sheet at the tops of integral plastic shelf fronts. This door panel likewise does not have any integral loop portions that provide a 360 degree door handle or any other portions capable of doing so.